In recent years, outdoor lighting such as street lighting, parking lot lighting and area lighting has been mounted on higher and higher poles enabling more luminaires to be mounted on a single pole than heretofore possible reducing the amount of individual poles that must be installed to obtain the same surface lighting. This reduction in the number of poles is desirable adjacent highways especially at intersections since fewer poles reduce the accident hazard to motorist.
These newer poles have obtained heights of 150 feet or more which makes the replacement of the bulb or lamps inaccessable to conventional bucket trucks or "cherry pickers" heretofore used for replacing the bulbs of conventional height lighting poles. Likewise, it is impractical to have built-in or removable ladders attached to the exterior of the pole to enable maintenance personnel to ascent to the top of such poles to service the luminaires.
To meet this difficult problem of bulb replacement and general maintenance, a number of devices have been involved. First, the individual lights were suspended by steel cables which pass through the hollow pole and over pulleys at the top so that each light could be lowered to the ground when desired simply by unwinding a sufficient length of cable connected with the individual light. The problem with this arrangement was that lights simply hung from individual steel cables tended to be blown around or sway in the wind causing cable wear and damage to the light by the continuous movement. Also, over an extended period of time the steel cables tended to stretch causing the lights to be lower than the desired height.
A later approach was to mount several of the lights on a movable carrier or support ring which was lowered to the ground by internal steel cables to permit access to the lights after which the ring was raised by the same cables to the normal height where they were latched onto a fixed support or platform permanently secured to the top of the pole. Some examples of such multiple luminaire support rings and the lower and raising system therefore are shown in U.S. Pat. Nos. 3,801,813; 3,862,744; 3,958,116; 4,001,573; 4,025,782; 4,228,488; 4,237,530; and 4,348,717.
However, when utilizing such a ring-like luminaire support it must remain centered around the support pole as it travels up and down the pole especially adjacent the top of the pole where it is located. Alignment is critical at the top of the pole to insure cooperative latching with the associated latching mechanism mounted on the fixed top support. This centering and alignment of the support ring is difficult to achieve even on relatively calm days due to wind forces on the ring as it obtains substantial heights on the pole.
One type of construction for overcoming the centering and stabilizing problem has been the use of a plurality of individual centering elements each of which is biased into engagement against the pole by springs. Usually three or four such biased elements have been used in such installations. One of the problems with such devices is that as the support ring moves off center, one of the stabilizing arms or elements attempts to recenter the support as intended. However, the remaining stabilizing arms provide a counterforce opposing the restoring force which actually reduces the effectiveness of the centering mechanism.
Another problem with such spring controlled stabilizing devices is that they do not exert a constant linear force on the pole as the pole diameter varies. An extremely high pole may vary in size from a diameter of several feet at the bottom to only several inches at the top. Tension or compression coil springs or other type springs used for applying the biasing force on the centering and stabilizing elements are not linear elements and therefore cannot exert a linear force. The force exerted is less as the spring is stretched and the stabilizer arms moved further away from the tensioning element as the pole diameter decreases. Thus, in the area where the greatest stabilizing force is required adjacent the pole top, the force exerted by the stabilizing members is lowest due to the use of springs.
Still another problem with known stabilizing and centering devices is that if the ring moves off center, even momentarily, one of the stabilizing arms may move out of contact with the pole and move beyond the pole in the biasing direction preventing the ring from returning to its trapped position between the stabilizing arms even after it attempts to return to its on-center position. Such movement of the arm could result in complete stopage of the ring movement requiring a difficult maintenance procedure to be performed on the ring to place the arms on the correct side of the pole to enable the ring to move freely vertically along the pole. U.S. Pat. No. 3,847,333 attempts to overcome this centering and stabilizing problem by providing a plurality of arms which are engaged with the hole and which act in unison by a plurality of connecting rods. However, the device of this patent still uses a spring to apply the tensioning force which will not provide the desired linear tensioning force. U.S. Pat. No. 4,348,717 shows another type of luminaire support ring centering device which uses torsion springs in combination with meshing gears in an attempt to achieve a uniform engagement. Again, the use of springs will not enable the linear constant tension to be achieved.
U.S. Pat. No. 4,092,707 discloses a centering and stabilizing device which uses the control cables for applying a force to a plurality of centering arms. However, the structure of this patent is relatively complicated and expensive and requires a parallelogram type linkage for moving the arms into contact with the pole. Also the pole contacting rollers are mounted on the outer end of the arms and could become disengaged from the pole requiring a costly maintenance procedure for correcting the situation.
Therefore the need has existed for an improved inexpensive, relatively simple stabilizing and centering device for a luminaire support ring which provides for a constant linear tensioning force of the stabilizing elements against the pole regardless of the changing pole diameter and vertical position of the support ring on the pole.